<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        ul {
            display: flex;
            border-bottom: 2px solid #e01222;
            padding: 0 10px;
        }

        li {
            width: 100px;
            height: 50px;
            line-height: 50px;
            list-style: none;
            text-align: center;
        }

        li a {
            display: block;
            text-decoration: none;
            font-weight: bold;
            color: #333333;
        }

        li a.active {
            background-color: #e01222;
            color: #fff;
        }
    </style>
</head>

<body>
    <div id="app">
        <ul>
            <!-- 动态切换类名使用对象属性值一定要是布尔值 -->
            <!-- 使用函数方式判断 -->
            <li v-for="e in list" :key="e.id"><a :class="{active:key===e.id}" @click="fn(e.id)" href="#">{{e.name}}</a></li>
        </ul>
    </div>
    <script src="vue.js"></script>
    <script>
        const app = new Vue({
            el: '#app',
            data: {
                // 默认第一个高亮
                key:1,
                list: [
                    { id: 1, name: '京东秒杀' },
                    { id: 2, name: '每日特价' },
                    { id: 3, name: '品类秒杀' }
                ]
            },
            methods:{
                fn(id){
                    this.key=id
                }
            }
        })
    </script>
</body>

</html>